Due to its movement in orbit, the faces of a spacecraft or satellite are subject to variations in the flux of the sun's rays depending on their orientation and their distance from the sun. Thus, certain faces of the craft do not receive the same amount of thermal energy over a twenty-four hour period and over the seasons.
For example, in a known manner and as shown more specifically in FIG. 1, a spacecraft of the geostationary satellite type 1 comes in the form of a parallelepipedal housing 2 rotating in an orbit 3 around the Earth 4 and always has the same face turned towards the Earth, such face being called the Earth face 5A, the opposite and parallel face to the Earth face 5A being called the anti-Earth face 5B. The North face 6 and the South face 7 of the housing are both opposite each other, parallel to each other and perpendicular to the North-South axis of the Earth 4, whilst the East 8 and West 9 faces are another two opposite faces, parallel to each other and perpendicular to the direction of movement of the spacecraft 1. Because of the nature of the geostationary orbit, the North 6 and South 7 faces are relatively unexposed to the rays emitted by the sun 10 compared with the East 8 and West 9 faces, which are alternately exposed to such rays during an orbital revolution. Normally, the North 6 and South 7 faces are the faces to which solar panels 11 are attached and the East 8 and West 9 faces are the faces to which communications antennae are attached.
The temperature variations from one face to another and of a single face over time limit the heat dissipation capacity of these faces. Thus, a face exposed to the sun will not release heat or will release less heat compared to a face located in the shade or receiving few light rays.
As a result, in order to enable the control of the heat flows in a satellite, it is necessary to provide means allowing for the dissipation of the thermal energy received by one of the hot faces of the satellite.
To enable such control and dissipation of the thermal energy, radiating panels, capable of radiating the power dissipated into space whilst minimizing the solar fluxes absorbed when these panels are exposed to the sun, are provided on faces of the satellite.
In a known manner, the North and South faces are used for heat dissipation due to the fact that they receive a small quantity of solar flux that is relatively constant over time.
As a result, it is standard practice to place on these North and South faces of the satellite heat-dissipating units known as “hot sources” such as a travelling-wave tube or OMUX (output multiplexer), which must also be thermally controlled by dissipation of their thermal energy by means of these radiators or radiating panels, when they are operational.
In order to allow for greater heat dissipation, the radiating surface would have to be increased. However, the surfaces that can be used for thermal radiation are limited by the volume available in the space launcher and the components already provided for on the surface of the satellite, such as the antennae.
Thus, because the thermal power available is limited, one of the main challenges for telecommunications satellite manufacturers is obtaining the best compromise between the power dissipated, the radiating surfaces and the mass of the satellite.
In order to increase the quantity of heat that can be dissipated, it is standard practice to provide within the satellite means of transferring heat from a hot face to a colder face that can dissipate more heat.
Thus, in order to enable the dissipation of heat from one face of the satellite to another, document U.S. Pat. No. 5,806,803 presents a system of heat pipes linking one face of a satellite to another opposite parallel face of the satellite by passing through an internal transverse panel. However, this system is relatively complex to implement and has constraints with regard to internal space occupied.
According to the same principle, that is the direct connection of two parallel opposite faces of a satellite to each other by means of a system of heat pipes, document US 2002/0139512 presents a system of heat pipes transversely linking the East face to the West face of the satellite in such a way as to share the thermal load between these two faces.
According to document U.S. Pat. No. 6,073,888, a heat flow control system is incorporated by placing radiators on the North, South, East and West faces and connecting them to a thermal load or dissipating units by means of Variable Conductance Heat Pipes (VCHP) or Diode Heat Pipes (DHP). However, this system is also complex to implement and poses incorporation constraints in terms of mass and volume, which represent a major restriction on its use.
Document U.S. Pat. No. 6,073,887 discloses a heat flow control system based on heat pipes in which a coolant circulates, that link certain faces of the satellite to each other and allow for the East and West faces to be used as radiating faces on which heat-emitting electronic equipment can be placed, in addition to the North and South faces on which such equipment is already installed. The production of a heat pipe loop connecting the East, West, Earth and anti-Earth faces is thus envisaged, in such a way as to control the thermal power on all of the faces.
This document does not however envisage enabling greater heat dissipation from the North and South faces, but conversely increasing the heat dissipation from the East and West faces by forming a heat pipe loop passing through the East, West, Earth and anti-Earth faces.
Document EP 1 468 911 presents a heat flow control system enabling the dissipation of these flows by means of the North, South, East and West faces based on a rack holding the equipment and heat transfer means to transfer the heat released by the heat-emitting electronic equipment to the North, South, East and West radiating panels, the heat transfer means being made up of at least one capillary pumped diphasic fluid loop.
However, according to this prior art it is necessary to add a structure, namely a rack, to hold the heat flow control system, which leads to constraints in terms of space occupied.
According to document U.S. Pat. No. 6,073,888, and more specifically the embodiment illustrated in FIG. 7 of that document, the production of a device for controlling the heat flows in a spacecraft that always has the same face turned towards the Earth is known, using a set of heat pipes placed either on the North face or on the South face, to which a thermal load is attached, and which is curved and extends over the East and West faces of the spacecraft. However, such a heat flow control device is not autonomous and cannot operate continuously over time. Indeed, it is necessary to provide thermal switches to enable the satisfactory operation of this device, which makes it difficult to implement and costly.
The production of a device for controlling the heat flows in a spacecraft is also known from document GB 2 270 666, using heat pipes linking the Earth face of the craft to the South and North faces, which results in the formation of a set of heat pipes linking three faces of the craft. However, this embodiment similarly does not allow for the production of a heat flow control device that is autonomous and can operate in all seasons.
It would therefore be particularly beneficial to produce a heat flow control system allowing for the dissipation of the heat emitted by electronic equipment placed on the North and South faces that does not require the addition of a transverse panel or a component arranged transversely between two opposite faces of the satellite.
It would therefore be particularly beneficial to produce a device for the thermal control of the power dissipated by the North and South faces of a geostationary satellite allowing for an increase in the number of pieces of heat-emitting electronic equipment on these faces whilst not generating constraints in terms of weight and space occupied.